In the textile industry, fiber slivers with a cross section consisting of a plurality of individual fibers are often measured for thickness, mass, density and/or moisture. This is necessary, e.g., in the area of drafting equipment in order to draft one or several fiber slivers to reduce the number or mass of their fibers in the cross-section of fiber slivers. It is then often the goal to produce an especially uniform fiber sliver, i.e., as much as possible, a fiber sliver with the same number of fibers or mass in the cross-section over its entire length. Drafting equipment of this type is used, for example, at the output of cards, in draw frames or spinning machines. In order to be able to level the sliver mass fluctuations of the fiber slivers, sliver sensors are provided, for example, on draw frames to measure sliver thickness or sliver mass and its fluctuations and to transmit this information to a control unit. At least one of the drafting elements of the draw frame is actuated by the control unit. In addition, an inspection is conducted frequently at the output of the drafting equipment to check whether the drafting process has taken place as desired, i.e., whether the mass of the fiber sliver has been leveled out.
To measure the sliver thickness fluctuation, mechanical scanning in particular is known. This mechanical scanning is at a disadvantage at extremely high delivery speeds of over 1,000 meters per minute, as is common in modern high-performance draw frames. Furthermore, the intensive mechanical compression required with mechanical sensors has a negative effect on the subsequent drafting process.
In addition to mechanical scanning of the sliver thickness fluctuations, scanning systems such as optical rays that penetrate the sliver thickness without contact, capacitive or pneumatic measuring methods, X-rays or similar methods have become known. These methods have however individual disadvantages that made them seem unsuited until now for continuous industrial application in the textile industry.
A microwave sensor has found to be an especially advantageous sensor to measure fiber sliver quality. The thickness, mass, density and/or moisture of one or several fiber slivers moving in relation to the sensor can be ascertained very reliably by means of microwave sensors. The sensor supplies a large number of signals per time unit, providing information on the current state of the (at least one) fiber sliver. The signals are transmitted in digital form and per time unit by the microwave sensor, or more precisely, by the microwave resonator, to a downstream high-frequency installation. In such a case, the fact that as the time-dependent signals are assigned to the proper location in the fiber sliver, a great computing expenditure is disadvantageously required because of the great quantity of data supplied. Furthermore, the assignment of the signals to the point on the (at least one) fiber sliver must take place exactly at the point in time at which it is in the drafting equipment. This is difficult to achieve by means of a microwave sensor and at reasonable cost, especially with very rapidly running fiber slivers.
Furthermore, if a microwave sensor such as is known for the measuring of moisture of cigarette paper is used in a conventional textile machine, e.g., a draw frame of model RSB-D 35 of the Rieter company, the first digital signals delivered by the output of the high-frequency device are analyzed for frequency shift and half-intensity width, and the corresponding values are converted by means of a D/A converter into analog signals, and these analog signals are then switched to the leveling computer of the draw frame which is provided at its input with an A/D converter. The digital output data of the leveling computer is then in turn converted into analog signals by means of a D/A converter, and are locked on to the analog input of the servo leveler which controls the lower input and central rollers. This expensive procedure is costly and subject to errors, because of the occurrence of the undesirable phase shift and quantization errors.